Article ID: 319108 - View products that this article applies to.
When you try to establish a virtual private network (VPN) connection, you may receive the following error message:
Error 800: Unable to establish connection
This issue may be caused by a router that has outdated firmware. For example, this issue may occur if you are using a Cisco router with firmware that is dated 2000 or earlier.
To verify that this is the cause, look at a network trace. The Cisco device advertises a 0 window size in the TCP handshake on port 1723.
To resolve this issue, contact the manufacturer of the router for possible upgrades.
For additional information about how to configure VPN connections in Windows XP, click the article numbers below to view the articles in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/314076/EN-US/ )HOW TO: Configure a Connection to a Virtual Private Network
(http://support.microsoft.com/kb/305550/EN-US/ )HOW TO: Configure a VPN Connection to Your Corporate Network in Windows XP Professional